Pedigree Charts The family tree of genetics

Pedigree Charts I II III

What is a Pedigree?  A pedigree is a chart of the genetic history of family over several generations.  Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree Female Male

Connecting Pedigree Symbols Examples of connected symbols: Couple

Connecting Pedigree Symbols Examples of connected symbols:

Example  What does a pedigree chart look like?

Symbols in a Pedigree Chart Affected Autosomal carrier Deceased

Interpreting a Pedigree Chart Determine if the pedigree chart shows an autosomal or X-linked disease. If most of the males in the pedigree are affected the disorder is X-linked If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree Charts  Is it Autosomal or X-linked?

Answer  Autosomal

Interpreting a Pedigree Chart Determine whether the disorder is dominant or recessive. If the disorder is dominant, one of the parents must have the disorder. If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Example of Pedigree Charts  Dominant or Recessive?

Answer

Example of Pedigree Charts  Dominant or Recessive?

Answer  Recessive

Autosomal recessive traits Trait is rare in pedigree Trait often skips generations (hidden in heterozygous carriers) Trait affects males and females equally Most common ones Cystic fibrosis Sickle cell anemia Phenylketonuria (PKU) Tay-Sachs disease

Autosomal dominant pedigrees Trait is common in the pedigree Trait is found in every generation Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

X-linked recessive pedigrees Trait is rare in pedigree Trait skips generations Affected fathers DO NOT pass to their sons, Males are more often affected than females

X-linked recessive traits ex. Hemophilia in European royalty

X-linked dominant pedigrees Trait is common in pedigree Affected fathers pass to ALL of their daughters Males and females are equally likely to be affected

X-linked dominant diseases X-linked dominant diseases are extremely unusual Often, they are lethal (before birth) in males and only seen in females ex. incontinentia pigmenti (skin lesions) ex. X-linked rickets (bone lesions)

What is the inheritance pattern? What is the genotype of III-1, III-2, and II-3? What are the odds that IV-5 would have an affected son?

Summary  Pedigrees are family trees that explain your genetic history.  Pedigrees are used to find out the probability of a child having a disorder in a particular family.  To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.